I read that certain marinades do tenderize meat, but the trouble is that they only tenderize the surface. It was suggested that injecting meat with the marinade would work.

Following the advice in the book, I used vinegar and fruit enzyme tenderizer, along with flavorings. I injected a roast with great zeal, in hundreds of places. The holes alone should have tenderized the meat somewhat.

The meat came out tougher than usual, not more tender. It did not taste better, either.

I have since read that vinegar actually toughens meat.

My next experiment will follow the advice that DAIRY is the superior meat tenderizer.

in Italy, motorist don't stop at red lights, simply because they define "red" as simply another shade of "green"

same with "marinades"

there's the point of "adding flavor(s)" and there's the point of "tenderizing"

the goals are different, so one can completely discard the "acid" / "dairy" / everything.

pineapple juice does contain natural enzymes which are quite potent "meat breaker-downers" - whether they be acid, alcohol, dairy or moon-based-green-cheese, the p.j. properties are quite well known and documented.